This invention relates to compounds which are free radical initiators and hindered amine light stabilizers.
It is well known that many ethylenically unsaturated monomers are polymerized using free radical initiators, i.e., those having peroxide groups. It is also well known that many of the polymers resulting from the polymerization of such monomers are subject to degradation by ultraviolet light, and, therefore, require the presence of an ultraviolet light stabilizer to extend the useful life of such polymers. Normally, such stabilizers are added to the polymer by methods such as milling or other methods of physical mixing. In more recent times, techniques of copolymerization have been used in which unsaturated derivatives of certain ultraviolet light stabilizing compounds have been copolymerized with vinyl monomers to form a light stabilized polymer. The method of physically mixing the stabilizer and the polymer has always been unsatisfactory because the resulting two-phase system is incompatible. The stabilizing compound inevitably migrates to the surface of the polymer and becomes separated from the polymer by evaporation, leaching, or erosion.
The copolymerization technique is more satisfactory than physically blending because it provides a chemically bound stabilizer which is not removed by physical processes. This method, however, has many inherent disadvantages because of the chemical equilibria involved in copolymerization reactions. The comonomer supplying the stabilizer component must have its reactivity balanced against that of the principle comonomer and the concentrations of these two comonomers adjusted to produce a product having the desired amount of stabilizer. The copolymerization technique also normally produces a product having more stabilizer incorporated into the polymer than is necessary, and this increases the cost of the final product markedly. Furthermore, many of the stabilizer comonomers have a tendency to homopolymerize rather than to copolymerize and thereby result in a product lacking homogeniety.
Hindered amine light stabilizers (hereinafter called HALS) are a class of compounds known to prevent and/or retard the degradation of polymers in which they are incorporated. Many patents on HALS additives and monomers are in the prior art (e.g., U.S. Pat. No. 4,336,183). The HALS compounds of the prior art suffer from the disadvantages stated above for UV stabilizers in general. The low molecular weight HALS have an added problem because they are water soluble which prevents their use because they are so readily leached from the polymer substrate upon exposure to moisture. Most patents issued on HALS disclose methods for making high molecular weight HALS which are less susceptible to leaching. This increase in molecular weight introduces problems of compatibility with the polymer to be stabilized and enhancement of the loss of the HALS additive by exudation. Also, increasing the molecular weight may produce adverse effect in cost or physical properties, since a greater amount of additive is necessary to assure the proper level of hindered amine functional group (which may represent only a small part of the high molecular weight additive).
A specific class of HALS peroxides known in the patent literature is perketals bearing a cyclic HALS moiety (European Patent 56,699) and ammonium salts thereof (U.S. Pat. No. 4,499,273). These patents disclose the use of the perketals as crosslinking and vulcanization agents. In these patents, the peroxygen groups are bonded directly to the piperidine ring of the HALS. The fragmentation of perketals during the initiation process assures that this combination of HALS and perketal initiator would not effectively bond the HALS to the polymer. (S. W. Bukata, L. L. Zabrocki, I&EC Product Research and Development, 1964(3), pp 261-266; V. V. Zaitseva, A. I. Yurzhenko, J. Org. Chem. USSR, 4(8), pp 1350-1353 (1968)). A perketal in which the peroxygen groups are not bonded directly to the piperidine ring would leave the piperidine stabilizer intact after the initiation process. Such remote perketal groups are envisioned as part of the current invention.